This invention relates to carriers for semiconductor wafers and more particularly it relates to a closeable container for storing and transporting wafers.
Sealable enclosures, generally termed transport modules, have been utilized in the semiconductor processing industry for a number of years for storing and transporting wafers between processing steps and/or between facilities. Semiconductor wafers are notoriously vulnerable to damage from contaminants such as particles. Extraordinary measures are taken to eliminate contaminants in cleanrooms and other environments where semiconductor wafers are stored or processed into circuits.
For wafers in the range of 200 mm and smaller, containers known as SMIF pods (standardized mechanism interface) have been utilized to provide a clean sealed mini-environment. Examples of these pods are shown in U.S. Pat. Nos. 4,532,970 and 4,534,389. Such SMIF pods typically utilize a transparent box-shaped shell with a lower door frame or flange defining an open bottom and a latchable door. The door frame clamps onto processing equipment and a door on the processing equipment and the lower SMIF pod door closing the open bottom are simultaneously lowered downwardly from the shell into a sealed processing environment in said processing equipment. A separate H-bar carrier positioned on the top surface inside of the SMIF pod door and loaded with wafers is lowered with the pod door for accessing and processing said wafers. In such pods the weight of the wafers would be directly on the door during storage and transport.
The semiconductor processing industry is moving toward utilization of larger and heavier wafers, specifically 30 mm wafers. Transport modules for such modules, by way of developing industry standards, will utilize a front opening door for insertion and removal of the wafers as opposed to a bottom door that drops downwardly from the module. The door would not support the load of the wafers, rather a container portion which would include a clear plastic (such as polycarbonate) shell and other members for supporting the wafers molded from a low particle generating plastic (such as polyetheretherketone) would carry the load of the wafers. Such container portions necessarily are made from multiple components assembled together.
In handling and processing semiconductor wafers, static electricity is a continuing concern. Electrostatic discharges can damage or ruin semiconductor wafers. Therefore, means must be taken to minimize any such generation of potentials which may cause static electric discharges. H-bar carriers have been manufactured with conventional static dissipative materials such as carbon filled polyetheretherketone (PEEK) and polycarbonate (PC).
The developing industry standards for such 300 mm modules require a machine interface, such as a kinematic coupling, on the bottom of the module to repeatedly and with precision align the module with respect to the processing equipment. This allows robotic handling means to engage the door on the front side of the module, open the door, and with the necessary amount of precision grasp and remove specific horizontally arranged wafers. It is highly critical to have the wafers positioned at a particular height and orientation with reference to the equipment machine interface such that the wafers will not be located and damaged during the robotic withdrawal and insertion of said wafers.
Due to inconsistencies in molding plastic parts assembly of such plastic parts lead to inconsistencies, such as open cracks between parts and the stacking of the tolerances of each individual part leading to undesirable variations in critical dimensions.
Known front opening 30 mm transport modules utilize multiple component parts including multiple components between the equipment interface and the wafer supports. This can lead to difficulty in producing modules with acceptable tolerances between the wafer planes and the equipment interface. Additionally, such modules have a path to ground from the wafer shelves to the equipment interface through several different components including metallic screws.
The 30 mm wafers are substantially greater in size and weight than the 20 mm modules; therefore, a structurally stronger module for transporting batches of wafers is required. Typically with the 20 mm SMIF pods the module was simply carried manually by grasping the lower edges at the juncture of the shell door flange and the door. Handles have been provided on the top of the shell portion for bottom opening pods. For carrying the larger, heavier, and bulkier modules for 30 mm wafers side handles are appropriate. For certain applications, the movement of the 30 mm module may be exclusively by way of robotic means thus not requiring handles or other means for manually transporting the container. Thus, a robotic lifting handle should be provided and any manual lifting handles should be easily removable.
Additionally, due to the high susceptibility of wafers to contamination by particles, moisture or other contaminants it is ideal to have a minimal number of potential entry paths to the interior of the module. Paths or breaks in the plastic between the interior and exterior of the pod such as for fasteners or at the junction of separate component parts of the module are to be avoided. Any such path required should be adequately sealed.
Additionally, the use at any location in the pod of metallic fasteners or other metal parts are highly undesirable in semiconductor wafer carriers or containers. Metallic parts generate highly damaging particulates when rubbed or scrapped. Assembly of a module with fasteners causes such rubbing and scrapping. Thus, the use of transport modules requiring metal fasteners or other metal parts are to be avoided.